在UKIDSS星系团巡天中识别附近的T型矮星
Identifying nearby field T dwarfs in the UKIDSS Galactic Clusters Survey
摘要：
我们提出了两个新的晚T矮星的发现，在UKIRT红外深空巡天（UKIDSS）星系团巡天（GCS）数据发布2（DR 2）中确定。这些T型矮星是位于UKIDSS GCS瞄准的恒星形成区和疏散星团视线范围内的老T型矮星。它们分别朝向Alpha Per星团和猎户座复合体，从五个过滤器中调查的54平方度的搜索中找到。光度候选人拿起双色图，在一个非常类似的方式从UKIDSS大面积调查（LAS），但利用Z过滤器所采用的GCS提取的候选人。这两个候选者都表现出近红外J带光谱，具有晚T矮星的特征甲烷和水吸收带。我们推导出T6.5+/-0.5和T7+/-1的光谱类型，并分别估计UGCS J030013.86+490142.5和UGCS J053022.52-052447.4的光度距离小于50 pc。在GCS中发现的T矮星的空间密度似乎与UKIDSS大区域巡天中发现的更大区域相一致，表明在6-11平方度内有一颗T矮星。最后一个由GCS测量的区域，在5个通带中测量1000平方度，将允许LAS搜索区域扩大25%，增加发现超冷棕矮星的可能性，并在深度测量中提供旧场棕矮星污染的最佳估计，以识别疏散星团和恒星形成区域中的此类天体。
英文摘要：
We present the discovery of two new late-T dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 2 (DR2). These T dwarfs are nearby old T dwarfs along the line of sight to star-forming regions and open clusters targeted by the UKIDSS GCS. They are found towards the Alpha Per cluster and Orion complex, respectively, from a search in 54 square degrees surveyed in five filters. Photometric candidates were picked up in two-colour diagrams, in a very similar manner to candidates extracted from the UKIDSS Large Area Survey (LAS) but taking advantage of the Z filter employed by the GCS. Both candidates exhibit near-infrared J-band spectra with strong methane and water absorption bands characteristic of late-T dwarfs. We derive spectral types of T6.5+/-0.5 and T7+/-1 and estimate photometric distances less than 50 pc for UGCS J030013.86+490142.5 and UGCS J053022.52-052447.4, respectively. The space density of T dwarfs found in the GCS seems consistent with discoveries in the larger areal coverage of the UKIDSS Large Area Survey, indicating one T dwarf in 6-11 square degrees. The final area surveyed by the GCS, 1000 square degrees in five passbands, will allow expansion of the LAS search area by 25%, increase the probability of finding ultracool brown dwarfs, and provide optimal estimates of contamination by old field brown dwarfs in deep surveys to identify such objects in open clusters and star-forming regions.
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